Updated Oma with 1,100 words! In it, you get started drilling dat azz. This scene's going to be a bit longer for PC cock/no cock variants, since it's kinda hard to write fucking a butt with a dick and making it flow seamlessly for PCs that don't have one.
“Oooh, yeah,” [oma.sisName] sighs, her body sinking into the plush material of the furniture as she relaxes underneath the feeling of you eating her ass. She slowly-but-insistently backs her ass against you, pushing you deeper, causing your nose to ride up the crack of her cheeks[pc.hasTail| until it bumps against the underside of her tail]. Your hands clamp onto the meat of her butt, your fingers sinking into the [pc.skinFurScalesNoun], giving you a bit extra to play with, and all she does is moan and writhe to your touch.
Every time you’re here, face-deep inside your own sister’s ass and rimming her star like it was candy, it brings you back to the first time you and [oma.sisName] first discovered you had feelings for each other – or, rather, the first time you acted on it. You were both shy, nervous creatures, knowing that what you were doing was wrong, and that if you moved too quickly or if you made too much noise, you’d be found out, and your lives would be over. Realizing that your soul mate was your sibling was an important turning point for you both.
And now, not only are you eating her ass with all the subtlety of an elephant fighting a bull, but your mother is lying in a sexually-exhausted heap on the floor beside you, having been fucked into a twitching, gasping, senseless mess. Life’s funny that way.